In general, each device that is introduced into the different body cavities has specific physical properties that are associated with the requirements for its intended use (e.g. angiography catheters, angioplasty balloon, ultrasonic transducer). In addition to the constrains imposed by the intended use, the geometry of such devices is dictated by the physical characteristics of the target position (e.g. blood vessels, atrium, ventricle, bladder, uterus etc.). Similarly, the means of introduction into the target position dictated the mechanical properties of the device and particularly its shaft (e.g. stiffness of the shaft, flexibility of the tip).
For example, pacing electrodes are introduced into the right ventricle or atrium to deliver electrical energy into the cardiac muscle. The conductors that connect the electrodes to an external or implantable pacemaker need to pass through the venous system to endure remarkable mechanical stress, causing probable fatigue due to the cardiac contractions. In order to impart the electrode lead durability the leads are constructed in coil structures that are very flexible and have very high fatigue resistance. The flexibility of the pacemaker lead makes it a difficult task to introduce it into the heart. A popular method of insertion employs a stiffening stylet, which is inserted into the lead during the deployment of the lead and thus increasing the stiffness during the insertion process. Once the lead has been positioned, the stylet is withdrawn and the lead regains its soft nature.
A different device that is introduced into the heart is the angioplasty balloon. The balloon is introduced into the coronaries, inflated at the desired location and then removed. The functional requirement for the balloon is to be capable of inflation and deflation at high reliability. To do so, a tube is connected between the pump and the balloon used for transferring the pressurized air to the balloon. In addition, the balloon needs to be inserted to its target location and thus the tube has a stiff structure to allow its navigation in the blood vessels from the proximal end located externally to the body.
In both examples the stiff body is required only for the insertion process and is not required for the proper operation of the devices once in place.
When administering interventional medical treatment within the human vasculature, or other body ducts, it is sometimes needed to perform a fast exchange of catheters during the operation. In practicing angioplasty, for example, it is often required to exchange one dilatation catheter with another. The exchange must, of course, be carried out fast, to avoid long exposure of the patient's open vasculature to possible infection, and shorten surgery time.
In the known "over-the-wire" catheterization procedure it is necessary to use a long guidewire, typically of 300 cm, which requires two operators to perform the procedure. This procedure is lengthy and prone to mistakes by the operators, as the device may accidentally touch the floor and may be subjected to contamination, which may even require repeating the catheterization procedure again.
In U.S. Pat. No. 5,357,978 (Turk), filed Jan. 12, 1993, an over-the-wire PTCA (Percutaneous Transluminal Coronary Angioplasty) balloon catheter was disclosed, having a guiding wire external to the shaft for slidably mounting over the guidewire. The guiding means has at least two loops, and a guidewire loading attachment between the pair of loops, which snaps onto the shaft of the balloon catheter.
In U.S. Pat. No. 5,040,548 (Yock), filed May 24, 1991, it was disclosed an angioplasty method consisting of the following steps: inserting a guiding catheter within the patient's cardiovascular system, disposing a guidewire within the inner lumen of said guiding catheter, disposing within the inner lumen of the guiding catheter a dilatation catheter having beside its lumen for directing the inflation liquid to the balloon a second shorter lumen, extending through the interior of the balloon, in which the guidewire is slidably disposed; advancing the dilatation catheter within the patient's coronary artery over the guidewire; withdrawing the dilatation catheter over the guidewire and removing it from the guidewire. In this patent, instead of using the "over the wire" approach which requires long exchange wires, the invention utilize a "monorail" approach that allows performing the procedure with shorter exchange wires. This is due to the basic difference between an "over the wire" approach and the "monorail" approach. The engagement between the angioplastic device and the exchange wire in a typical "over-the-wire" device is present throughout the entire length of the angioplastic device while in a typical "monorail" device the attachment between the angioplasty device and the guidewire is achieved over a short segment at the distal tip of the angioplastic device.
In U.S. Pat. No. 5,389,087 (Miraki) filed Jun. 29, 1992, it was disclosed a fully exchangeable over-the-wire catheter with rip seam and gated side port. The catheter is provided with a lumen adapted to receive a guidewire throughout the longitudinal extent of the tubular shaft. The tubular shaft may be provided with a longitudinal rip seam extending into the lumen, which enables the catheter to be peeled from the guidewire during removal and exchange procedures. Optionally the catheter is also provided with one or more side ports into the guidewire lumen.
In U.S. Pat. No. 5,578,009 (Kraus et al.), filed Jul. 20, 1994, it was disclosed an elongated rod, terminating in an abutment device with a lumen for passing of a guidewire, used to push an angioplasty balloon along the guidewire. U.S. Pat. No. 5,718,680 (Kraus et al.), filed as continuation-in-part to U.S. Pat. No. 5,578,009 on Aug. 21, 1996, disclosed a method for placing an angioplasty balloon in accordance with the device disclosed in U.S. Pat. No. 5,578,009.
The advantage of the "monorail" approach comes at the cost of increased risk for damaging the guiding wire during the pushing operation. The proximal end of the advancing angioplastic device may be at some distance from the guide wire and cause it to bend, creating a "kink" that may render the guidewire not fit for further use, and prevent completing the positioning of the angioplasty device in its target location. The invention descried in U.S. Pat. No. 5,040,548 utilizes a large diameter-guiding catheter through which the short guide wire and the angioplastic device are inserted. This catheter minimizes the operational diameter, reducing the distance between the body of the angioplastic device and the guidewire and thus minimizes the above-mentioned potential complication. Thus the employment of a monorail device seems to solve the problem of long exchange wires at the cost of increased diameter of the guiding catheter. There is therefore a need for an apparatus that overcomes both difficulties.